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Rh a narrow groove 3 ft. 9 in. deep along the bottom of the coal, which is afterwards broken down in the usual way. Three times more coal can be got by four men with it in a day than they can get without it. The waste of coal in the operation of holing is reduced by two-thirds. That is to say, if this machine could be used in all the pits in the kingdom, there would be an actual saving of 8,000,000 to 9,000,000 tons of coal per annum! There are other (hydraulic) coal-cutting machines at work in collieries in the north of England, which are equally economical, and which will, like Mr. Firth's machine, work narrow seams at a profit which it would not pay to work by hand; but they do not possess the important ventilating power, which is one of its chief recommendations. The expansion of the air not only lowers the temperature, but it drives all the gas away from the working-face. That this is done is sufficiently proved by the fact that there has not been a single explosion at West Ardsley since the machine has been in use, although there were many minor ones before it was introduced.

Who can say the condition of our coal-mines is satisfactory when such results are attainable? Yet who can touch the evil? The man who shall succeed in improving their ventilation will be a greater benefactor to his country than Sir Humphrey Davy, and will well deserve public reward; although, perhaps, he will be more likely to incur unmerited odium.